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The behavior of a dam during initial filling of its impounded reservoir, which can be characterized not only by the ascent of the water level, but also by warming of the bed of the dam and change in its physico-mechanical properties during filling of the reservoir as a result of its contact with the water, is analyzed. It is demonstrated in this period that it not so much the hydrostatic pressure of the water as the change in the temperature regime in the near-surface zone of the bed that has a major determining effect on deformation of the near-contact zone of the bed.When constructing water-development works in regions of permafrost propagation, it is necessary in the initial filling of the reservoir to consider the possibility of pronounced changes in the phsyico-mechanical characteristics of their rock beds. Serving as the basic factor for the heat transfer of positive temperatures into the rock bed of the dam, the water of the reservoir will, as a result of warming of the bed, contribute to its increased deformability, increase in porosity, and fissuring, and reduction in strength. Moreover, all this will occur over time in the process of warming, making it impossible to previously construct a geomechanical model for prediction of the behavior of the structure during initial filling of the reservoir.The first filling of the reservoir at the Boguchany HPP, when despite the increase in hydrostatic pressure on the body of the rock-fill dam, its displacements were recorded in the direction of the upper pool, and an increase in settlements was noted as the air temperature rose with the upper pool at an essentially constant level, may serve as one of the characteristic examples of such behavior [1].The rock-fill and concrete dams at the Boguchany HPP were constructed under complex natural-climatic conditions, which have exerted a considerable influence on the condition of the structural components of the dam. The maximum temperature differential at the damsite during initial filling of the reservoir was of the order of 50°C (from +20 to -30°C), just at that time when the temperature of the bed in the near-contact zone prior to start of filling of the reservoir fluctuated from +1 to +5°C.The first pronounced increase in the temperature of the bed of the dam was noted after the start of the initial filling of the reservoir on 16 April 2013 (Fig. 1); here, it was noted not immediately after the start of ascent of upper-pool level, but after approximately one month, during which warming of the near-contact zone of the bed of the concrete dam, which is comprised of a dense dolerite, was initiated. Temperatures of the bed were measured by PTS-60 string temperature transducers in holes. Figure 2 shows diagrams of the temperature rise in the bed of Section No. 14 of the concrete dam and the concurrent increase in its settlement. It is obvious that penetration of reservoir water into the bed of the dam had caused the temperature to rise in its near-contact zone, exerting a significant influence on the behavior of the concr...

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